<!DOCTYPE html>
<html lang="cn">
<head>
    <meta charset="UTF-8">
    <title>Document</title>
    <style>
        body{margin:0px;background-color: #fff;}
        #bg{width:100px;height:100px;background-color: #fff}
        #url a{color:#fff;}
    </style>

</head>
<body onkeydown=doKey(event) >
    <div id="bg">
        <div id="url">
            
        </div>
    </div>
</body>

</html>
 <script>
        var puts=new Array();

        var T;

        var Need = 0;
        
        var link = `<a href="http://www.baidu.com" target=_blank>神秘链接</a>`;

        function doKey(e)
        {
            if(e.which)
            {
                Need = 1;
                
                puts.push(e.which);
            }
            
            fin();

            doReset();
        }

        function fin()
        {
            if(puts.toString()=="38,38,40,40,37,39,37,39,66,65")
            {
                

                var bg = document.getElementById("bg");

                console.log(bg.style);

                bg.style.backgroundColor = "#000";

                document.getElementById("url").innerHTML = link;
            }
        }

        function doReset()
        {
            if(Need==1)
            {
                setTimeout(function clearT(){puts=[];},3000);

                Need=0;
            }
        }
       
    </script>